[boost-context] build failure on unified builds

[simtind]

Host Environment

• OS: Mac OS 11.6
• Compiler: XCode 12.4

To Reproduce
With the following triplet available as arm64-x64-osx:

# Creates unified MacOS binaries supporting both Arm64 and Intel X64 processors.
set(VCPKG_TARGET_ARCHITECTURE x86_64 arm64)
set(VCPKG_CRT_LINKAGE dynamic)
set(VCPKG_LIBRARY_LINKAGE static)

set(VCPKG_CMAKE_SYSTEM_NAME Darwin)
set(VCPKG_OSX_ARCHITECTURES x86_64 arm64)

Execute
./vcpkg install boost-context:arm64-x64-osx

Failure logs
From a manifest install that includes boost-context:

Installing 21/21 boost-context:arm64-x64-osx...
Building boost-context[core]:arm64-x64-osx...
-- [OVERLAY] Loading triplet configuration from: /opt/vcpkg_git/vcpkg-overlay-ports/triplets/arm64-x64-osx.cmake
-- Using cached boostorg-context-boost-1.79.0.tar.gz.
-- Cleaning sources at /Users/buran_ci/vcpkg/buildtrees/boost-context/src/ost-1.79.0-c7ed8111f4.clean. Use --editable to skip cleaning for the packages you specify.
-- Extracting source /Users/buran_ci/vcpkg/downloads/boostorg-context-boost-1.79.0.tar.gz
-- Using source at /Users/buran_ci/vcpkg/buildtrees/boost-context/src/ost-1.79.0-c7ed8111f4.clean
-- Including /Users/buran_ci/vcpkg/buildtrees/boost-context/vcpkg-b2-options.cmake
-- Found external ninja('1.10.2').
-- Getting CMake variables for arm64-x64-osx-dbg
-- Getting CMake variables for arm64-x64-osx-rel
-- Configuring arm64-x64-osx-dbg
-- Configuring arm64-x64-osx-rel
-- Building arm64-x64-osx-dbg
CMake Error at scripts/cmake/vcpkg_execute_build_process.cmake:129 (message):
    Command failed: /Users/buran_ci/vcpkg/downloads/tools/cmake-3.22.2-osx/cmake-3.22.2-macos-universal/CMake.app/Contents/bin/cmake --build . --config Debug --target install -- -v -j9
    Working Directory: /Users/buran_ci/vcpkg/buildtrees/boost-context/arm64-x64-osx-dbg
    See logs for more information:
      /Users/buran_ci/vcpkg/buildtrees/boost-context/install-arm64-x64-osx-dbg-out.log

Call Stack (most recent call first):
  installed/arm64-osx/share/vcpkg-cmake/vcpkg_cmake_build.cmake:74 (vcpkg_execute_build_process)
  installed/arm64-osx/share/vcpkg-cmake/vcpkg_cmake_install.cmake:16 (vcpkg_cmake_build)
  installed/arm64-osx/share/boost-build/boost-modular-build.cmake:136 (vcpkg_cmake_install)
  ports/boost-context/portfile.cmake:22 (boost_modular_build)
  scripts/ports.cmake:146 (include)


error: building boost-context:arm64-x64-osx failed with: BUILD_FAILED
Please ensure you're using the latest port files with `git pull` and `vcpkg update`.
Then check for known issues at:
    https://github.com/microsoft/vcpkg/issues?q=is%3Aissue+is%3Aopen+in%3Atitle+boost-context
You can submit a new issue at:
    https://github.com/microsoft/vcpkg/issues/new?template=report-package-build-failure.md&title=[boost-context]+Build+error
Include '[boost-context] Build error' in your bug report title, the following version information in your bug description, and attach any relevant failure logs from above.
    vcpkg-tool version: 2022-06-15-b0f08e40f8e8752dd0b260138ee078bd9599559c
    vcpkg-scripts version: 3d8f78171 2022-06-15 (12 hours ago)

You can also use the prefilled template from /Users/buran_ci/vcpkg/installed/vcpkg/issue_body.md.

cat /Users/buran_ci/vcpkg/buildtrees/boost-context/install-arm64-x64-osx-dbg-out.log
[1/2] cd /Users/buran_ci/vcpkg/buildtrees/boost-context/src/ost-1.79.0-c7ed8111f4.clean/build && /Users/buran_ci/vcpkg/installed/arm64-osx/tools/boost-build/b2 toolset=clang --user-config=/Users/buran_ci/vcpkg/buildtrees/boost-context/arm64-x64-osx-dbg/user-config.jam --stagedir=/Users/buran_ci/vcpkg/buildtrees/boost-context/arm64-x64-osx-dbg/stage --build-dir=/Users/buran_ci/vcpkg/buildtrees/boost-context/arm64-x64-osx-dbg runtime-link=shared link=static address-model=64 architecture=x86 target-os=darwin threadapi=pthread variant=debug --layout=system -sICU_PATH="ICU_PATH-NOTFOUND" abi=sysv binary-format=mach-o --with-atomic --with-random --with-date_time --with-filesystem --with-system --with-thread --with-chrono -j8 -sBOOST_ROOT=/Users/buran_ci/vcpkg/installed/arm64-osx/tools/boost-build -sBOOST_BUILD_PATH=/Users/buran_ci/vcpkg/installed/arm64-osx/tools/boost-build --debug-configuration --debug-building --debug-generators --ignore-site-config --hash -q debug-symbols=on -d +2 threading=multi stage

...


    "/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/c++" -x assembler-with-cpp -fPIC -g -isysroot "/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX11.1.sdk" -arch x86_64 -arch arm64 -D_DARWIN_C_SOURCE -m64 -O0 -fno-inline -Wall -g  -DBOOST_ALL_NO_LIB=1 -DBOOST_CONTEXT_SOURCE -I"../include" -I"/Users/buran_ci/vcpkg/installed/arm64-x64-osx/include" -c -o "/Users/buran_ci/vcpkg/buildtrees/boost-context/arm64-x64-osx-dbg/boost/build/c6e7fa824b7fcb2640207cf1bd4ce369/asm/ontop_x86_64_sysv_macho_gas.o" "../src/asm/ontop_x86_64_sysv_macho_gas.S"

../src/asm/ontop_x86_64_sysv_macho_gas.S:32:10: error: unknown token in expression
    movq %rdx, %r8
         ^
../src/asm/ontop_x86_64_sysv_macho_gas.S:32:10: error: invalid operand
    movq %rdx, %r8
         ^
../src/asm/ontop_x86_64_sysv_macho_gas.S:34:15: error: unexpected token in argument list
    leaq -0x38(%rsp), %rsp
              ^
../src/asm/ontop_x86_64_sysv_macho_gas.S:37:14: error: unknown token in expression
    stmxcsr (%rsp)
             ^
../src/asm/ontop_x86_64_sysv_macho_gas.S:37:13: error: invalid operand
    stmxcsr (%rsp)
            ^
../src/asm/ontop_x86_64_sysv_macho_gas.S:38:15: error: unexpected token in argument list
    fnstcw 0x4(%rsp)
              ^
../src/asm/ontop_x86_64_sysv_macho_gas.S:41:10: error: unknown token in expression
    movq %r12, 0x8(%rsp)
         ^
../src/asm/ontop_x86_64_sysv_macho_gas.S:41:10: error: invalid operand
    movq %r12, 0x8(%rsp)
         ^
../src/asm/ontop_x86_64_sysv_macho_gas.S:42:10: error: unknown token in expression
    movq %r13, 0x10(%rsp)
         ^
../src/asm/ontop_x86_64_sysv_macho_gas.S:42:10: error: invalid operand
    movq %r13, 0x10(%rsp)
         ^
../src/asm/ontop_x86_64_sysv_macho_gas.S:43:10: error: unknown token in expression
    movq %r14, 0x18(%rsp)
         ^
../src/asm/ontop_x86_64_sysv_macho_gas.S:43:10: error: invalid operand
    movq %r14, 0x18(%rsp)
         ^
../src/asm/ontop_x86_64_sysv_macho_gas.S:44:10: error: unknown token in expression
    movq %r15, 0x20(%rsp)
         ^
../src/asm/ontop_x86_64_sysv_macho_gas.S:44:10: error: invalid operand
    movq %r15, 0x20(%rsp)
         ^
../src/asm/ontop_x86_64_sysv_macho_gas.S:45:10: error: unknown token in expression
    movq %rbx, 0x28(%rsp)
         ^
../src/asm/ontop_x86_64_sysv_macho_gas.S:45:10: error: invalid operand
    movq %rbx, 0x28(%rsp)
         ^
../src/asm/ontop_x86_64_sysv_macho_gas.S:46:10: error: unknown token in expression
    movq %rbp, 0x30(%rsp)
         ^
../src/asm/ontop_x86_64_sysv_macho_gas.S:46:10: error: invalid operand
    movq %rbp, 0x30(%rsp)
         ^
../src/asm/ontop_x86_64_sysv_macho_gas.S:49:10: error: unknown token in expression
    movq %rsp, %rax
         ^
../src/asm/ontop_x86_64_sysv_macho_gas.S:49:10: error: invalid operand
    movq %rsp, %rax
         ^
../src/asm/ontop_x86_64_sysv_macho_gas.S:52:10: error: unknown token in expression
    movq %rdi, %rsp
         ^
../src/asm/ontop_x86_64_sysv_macho_gas.S:52:10: error: invalid operand
    movq %rdi, %rsp
         ^
../src/asm/ontop_x86_64_sysv_macho_gas.S:55:14: error: unknown token in expression
    ldmxcsr (%rsp)
             ^
../src/asm/ontop_x86_64_sysv_macho_gas.S:55:13: error: invalid operand
    ldmxcsr (%rsp)
            ^
../src/asm/ontop_x86_64_sysv_macho_gas.S:56:14: error: unexpected token in argument list
    fldcw 0x4(%rsp)
             ^
../src/asm/ontop_x86_64_sysv_macho_gas.S:59:13: error: unexpected token in argument list
    movq 0x8(%rsp), %r12
            ^
../src/asm/ontop_x86_64_sysv_macho_gas.S:60:14: error: unexpected token in argument list
    movq 0x10(%rsp), %r13
             ^
../src/asm/ontop_x86_64_sysv_macho_gas.S:61:14: error: unexpected token in argument list
    movq 0x18(%rsp), %r14
             ^
../src/asm/ontop_x86_64_sysv_macho_gas.S:62:14: error: unexpected token in argument list
    movq 0x20(%rsp), %r15
             ^
../src/asm/ontop_x86_64_sysv_macho_gas.S:63:14: error: unexpected token in argument list
    movq 0x28(%rsp), %rbx
             ^
../src/asm/ontop_x86_64_sysv_macho_gas.S:64:14: error: unexpected token in argument list
    movq 0x30(%rsp), %rbp
             ^
../src/asm/ontop_x86_64_sysv_macho_gas.S:66:14: error: unexpected token in argument list
    leaq 0x38(%rsp), %rsp
             ^
../src/asm/ontop_x86_64_sysv_macho_gas.S:70:10: error: unknown token in expression
    movq %rsi, %rdx
         ^
../src/asm/ontop_x86_64_sysv_macho_gas.S:70:10: error: invalid operand
    movq %rsi, %rdx
         ^
../src/asm/ontop_x86_64_sysv_macho_gas.S:73:10: error: unknown token in expression
    movq %rax, %rdi
         ^
../src/asm/ontop_x86_64_sysv_macho_gas.S:73:10: error: invalid operand
    movq %rax, %rdi
         ^
../src/asm/ontop_x86_64_sysv_macho_gas.S:78:9: error: unknown token in expression
    jmp *%r8
        ^
../src/asm/ontop_x86_64_sysv_macho_gas.S:78:9: error: invalid operand
    jmp *%r8
        ^
clang-darwin.compile.asm /Users/buran_ci/vcpkg/buildtrees/boost-context/arm64-x64-osx-dbg/boost/build/c6e7fa824b7fcb2640207cf1bd4ce369/asm/make_x86_64_sysv_macho_gas.o

    "/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/c++" -x assembler-with-cpp -fPIC -g -isysroot "/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX11.1.sdk" -arch x86_64 -arch arm64 -D_DARWIN_C_SOURCE -m64 -O0 -fno-inline -Wall -g  -DBOOST_ALL_NO_LIB=1 -DBOOST_CONTEXT_SOURCE -I"../include" -I"/Users/buran_ci/vcpkg/installed/arm64-x64-osx/include" -c -o "/Users/buran_ci/vcpkg/buildtrees/boost-context/arm64-x64-osx-dbg/boost/build/c6e7fa824b7fcb2640207cf1bd4ce369/asm/make_x86_64_sysv_macho_gas.o" "../src/asm/make_x86_64_sysv_macho_gas.S"

../src/asm/make_x86_64_sysv_macho_gas.S:32:10: error: unknown token in expression
    movq %rdi, %rax
         ^
../src/asm/make_x86_64_sysv_macho_gas.S:32:10: error: invalid operand
    movq %rdi, %rax
         ^
../src/asm/make_x86_64_sysv_macho_gas.S:35:10: error: invalid token in expression
    andq $-16, %rax
         ^
../src/asm/make_x86_64_sysv_macho_gas.S:35:10: error: invalid operand
    andq $-16, %rax
         ^
../src/asm/make_x86_64_sysv_macho_gas.S:39:15: error: unexpected token in argument list
    leaq -0x40(%rax), %rax
              ^
../src/asm/make_x86_64_sysv_macho_gas.S:43:10: error: unknown token in expression
    movq %rdx, 0x28(%rax)
         ^
../src/asm/make_x86_64_sysv_macho_gas.S:43:10: error: invalid operand
    movq %rdx, 0x28(%rax)
         ^
../src/asm/make_x86_64_sysv_macho_gas.S:46:14: error: unknown token in expression
    stmxcsr (%rax)
             ^
../src/asm/make_x86_64_sysv_macho_gas.S:46:13: error: invalid operand
    stmxcsr (%rax)
            ^
../src/asm/make_x86_64_sysv_macho_gas.S:48:15: error: unexpected token in argument list
    fnstcw 0x4(%rax)
              ^
../src/asm/make_x86_64_sysv_macho_gas.S:51:20: error: unexpected token in argument list
    leaq trampoline(%rip), %rcx
                   ^
../src/asm/make_x86_64_sysv_macho_gas.S:54:10: error: unknown token in expression
    movq %rcx, 0x38(%rax)
         ^
../src/asm/make_x86_64_sysv_macho_gas.S:54:10: error: invalid operand
    movq %rcx, 0x38(%rax)
         ^
../src/asm/make_x86_64_sysv_macho_gas.S:57:16: error: unexpected token in argument list
    leaq finish(%rip), %rcx
               ^
../src/asm/make_x86_64_sysv_macho_gas.S:60:10: error: unknown token in expression
    movq %rcx, 0x30(%rax)
         ^
../src/asm/make_x86_64_sysv_macho_gas.S:60:10: error: invalid operand
    movq %rcx, 0x30(%rax)
         ^
../src/asm/make_x86_64_sysv_macho_gas.S:67:10: error: unknown token in expression
    push %rbp
         ^
../src/asm/make_x86_64_sysv_macho_gas.S:67:10: error: invalid operand
    push %rbp
         ^
../src/asm/make_x86_64_sysv_macho_gas.S:69:9: error: unknown token in expression
    jmp *%rbx
        ^
../src/asm/make_x86_64_sysv_macho_gas.S:69:9: error: invalid operand
    jmp *%rbx
        ^
../src/asm/make_x86_64_sysv_macho_gas.S:73:10: error: unknown token in expression
    xorq %rdi, %rdi
         ^
../src/asm/make_x86_64_sysv_macho_gas.S:73:10: error: invalid operand
    xorq %rdi, %rdi
         ^
../src/asm/make_x86_64_sysv_macho_gas.S:75:5: error: unrecognized instruction mnemonic, did you mean: casl?
    call __exit
    ^
../src/asm/make_x86_64_sysv_macho_gas.S:76:5: error: too few operands for instruction
    hlt
    ^~~
clang-darwin.compile.c++ /Users/buran_ci/vcpkg/buildtrees/boost-context/arm64-x64-osx-dbg/boost/build/c6e7fa824b7fcb2640207cf1bd4ce369/posix/stack_traits.o

    "/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/c++" -x c++ -fPIC -g -isysroot "/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX11.1.sdk" -arch x86_64 -arch arm64 -std=c++11 -D_DARWIN_C_SOURCE -m64 -O0 -fno-inline -Wall -g  -DBOOST_ALL_NO_LIB=1 -DBOOST_CONTEXT_SOURCE -I"../include" -I"/Users/buran_ci/vcpkg/installed/arm64-x64-osx/include"  -c -o "/Users/buran_ci/vcpkg/buildtrees/boost-context/arm64-x64-osx-dbg/boost/build/c6e7fa824b7fcb2640207cf1bd4ce369/posix/stack_traits.o" "../src/posix/stack_traits.cpp"

...failed updating 2 targets...
ninja: build stopped: subcommand failed.

Additional context
Boost-build expects architecture=x86+arm64 to be set when compiling for unified binaries. Instead, vcpkg sets architeture=x86, and adds compile flags -arch x86 -arch arm64. Looks like this causes the x86 assembly files to be compiled for arm64.